Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $139.85   9.299%   $152.8547   $152.85   $152.85   $152.90  
  Purchase #2 $206.43   4.795%   $216.3283   $216.33   $216.35   $216.30  
  Purchase #3 $16.72   5.265%   $17.6003   $17.60   $17.60   $17.60  
  Purchase #4 $142.38   13.854%   $162.1053   $162.11   $162.10   $162.10  
  Purchase #5 $248.53   5.540%   $262.2986   $262.30   $262.30   $262.30  
  Purchase #6 $164.68   7.774%   $177.4822   $177.48   $177.50   $177.50  
  Purchase #7 $247.36   5.451%   $260.8436   $260.84   $260.85   $260.80  
  7 purchase totals = $1,165.95       $1,249.5130   $1,249.51   $1,249.55   $1,249.50